Cellulose acetate spinning process



United States Patent CELLULOSE ACETATE SPINNING PROCESS Francois I.Olmer, Morristown, N. 1., asslgnor to Celanese Corporation of America,New York, N. Y., a corporation of Delaware No Drawing. ApplicationNovember 24, 1950,

Serial No. 197,516

1 Claim. (CI. 18-54) This invention relates to filamentary materials andrelates more particularly to a process for the production of filamentarymaterials having a basis of cellulose acetate or other organic acidester of cellulose.

It is an important object of this invention to provide a process for theproduction of high tenacity filamentary materials having a basis ofcellulose. acetate or other organic acid ester of cellulose.

A further object of this invention isvtoyprovide an improved process forthe production of filamentary materials wherein a solution of celluloseacetate or other organic acid ester of cellulose is spun into acoagulating medium comprising a latent solvent incapable of dissolvingthe cellulose ester, but capable of swelling it to a considerableextent.

A still further object of this invention is to provide an improvedprocess for the production of filamentary materials wherein a solutionof cellulose acetate or other organic acid ester of cellulose is spuninto a coagulating medium comprising a mixture of carbon tetrachlorideand methylene chloride. I I

Another object of this invention is to provide a process for theproduction of filamentary materials wherein a solution of celluloseacetate or other organic acid ester of cellulose is spun into acoagulating medium comprising a mixture of carbon tetrachloride andmethylene chloride and the filamentary materials are passed, while stillwet with the coagulating medium, into a saponification bath.

Other objects of this invention will be apparent from the followingdetailed description and claim.

In the production of filamentary materials having a basis of.celluloseacetate or other organic acid ester of cellulose by the wet-spinningprocess, a solution of the filament-forming material in a suitablesolvent is pumped or otherwise forced through a spinning jet, having atleast one spinning orifice therein, into a liquid coagulating mediumwhich causes the filament-forming material to coagulate or set and whichextracts the solvent therefrom. It has previously been proposed toincrease the tenacity of the filamentary materials produced in thismanner by stretching said materials during the, spinning operation whilethey are still in a relatively plastic state. In this way, it ispossible to produce filamentary materials having tenacities of from 2 to5 or more grams per denier. However, the increase in the tenacity of thefilamentary materials is accompanied by a reduction in their elongation,so that it is diflicult to weave, knit or otherwise prgcess saidhigh-tenacity filamentary materials into textile a rics.

l have now discovered that by spinning a solution of cellulose acetateor other organic acid ester of cellulose into a coagulating mediumcomprising a latent solvent incapable of dissolving the cellulose ester,but capable of swelling it to a considerable extent, such as a mixtureof carbon tetrachloride and methylene chloride, and stretching saidfilamentary materials while they are still in a relatively plasticstate, it is possible to obtain products having both a high tenacity anda good elongation which may be converted without difficulty into textilefabrics. Thus, in accordance with the present invention a solution ofcellulose acetate or other organic acid ester of cellulose is pumped orotherwise forced through a spinning jet, having at least one spinningorifice therein, into a coagulating medium comprising a mixture of thetype specified above. The filamentary materials formed in this mannerare stretched while they are still in a relatively plastic state,

2,702,230 Patented Feb. 15, 1955 stretched during their production, thehigher the degree of stretch the higher the tenacity and the lower theelongation of the final product.

In' carrying out the process of the present invention, a spinningsolutionor dope is prepared by dissolving cellulose acetate or otherorganic acid ester of cellulose in a suitable solvent such as, forexample, acetone, acetonewater mixtures, 98:2% by -weight or 95:5% byweight, preferably in an amount sutficient to yield spinning dopecontaining from about 18 to 28% by weight of the filament-formingmaterial. The spinning dope, after being filtered to remove therefromall solid impurities, is spun into a coagulating medium containing, forexample, fr om about 10 to 25% by volume of carbon tetrachloride, theremainder being methylene chloride. As the spinning dope enters thecoagulating medium, the filament forming material is caused to set orgel and the solvent is extracted therefrom by the coagulating medium.Other coagulating media that may be employed include, for example,dichloroethane and tetrachloroethane alone; ethylene chloride, alone, oradmixed with carbon tetrachloride (95 :5% -by weight); chloroformadmixed with carbon tetrachloride (80:20% to :10% by weight) andmethylene chloride admixed with'benzene, toluene, -cyclohexane and thelike.

While the filamentary materials are still in a relatively plastic state,they are stretched to increase their length by about 1000 to 5000%. Thestretching may be effected by passing the filamentary materials over anumber of rollers immersed in the coagulating medium, each successiveroller having a higher peripheral speed than the preceding roller.Preferably, however, the stretching is effected by means of a positivelydriven roller which draws the filamentary materials from the coagulatingmedium at the proper speed. After the filamentary materials emerge fromthe coagulating medium they are dried, following which they may betwisted and wound onto a textile package or otherwise treated to preparethem for further use.

The coagulating medium is advantageously maintained at a temperature offrom about 0 to 30 C. depending upon its composition. When thecoagulating'medium is employed at the higher temperatures within thisrange,

say above about 25 C., the concentration of any cellulose ester solvent,such as methylene chloride, therein should be kept below the value atwhich excessive softening of the filamentary materials will take place,which, when multi-filament materials are being produced, may causethti:1 individual filaments thereof to coalesce, one with the 0 er.

To improve the tenacity and/or to modify the dyeing and other propertiesof the filamentary materials prepared in the manner set forth above, itis frequently desirable to saponify the cellulose acetate or otherorganic acid ester of cellulose, either partially or completely. Whilethe saponification may be effected by treating the dried filamentarymaterials with a suitable saponification bath, it has been found thatthe saponification may be effected more rapidly and more uniformly bypassing the filamentary materials through the saponification bath Whilethey are still wet with the coagulating medium. Thus, the filamentarymaterials may be passed directly from one container holding thevcoagulating medium into another container holding the saponificationbath, care being taken to avoid any substantial evaporation of thecoagulating medium from the filamentary materials as said materials passfrom one container to the other. A preferred method for efiecting thesaponification is to float a saponification bath immiscible with thecoagulating medium on the coagulating medium so that the filamentarymaterials will pass through said saponification bath as they emerge fromthe coagulating medium. In this way,

agcaaao the escr e of the coagulating medium from the filamentarymaterials before they enter the saponificatlon bath 18 substantiallyavoided and, in addition, the saponification bath acts to seal thecoagulating medium from the atmosphere ereby minimizing the loss of saidmedium through evaporation. When the saponification has progressed tothe desired extent, the filamentary materials are withdrawn from thesaponification bath and are washed to remove therefrom the products ofsaponification and the saponification bath and dried, following whichthey may be twisted and wound onto a textile package or otherwisetreated to prepare them for further use.

As the saponification bath there may be employed, for example, aqueoussolutions of alkaline materials such as sodium hydroxide,potassiumhydroxide or ammonium hydroxide, to which solutions there may be addedbuffering salts such as sodium acetate, potassium acetate or ammoniumacetate to make more uniform the action of said baths.

The process of this invention will now be described specifically inconnection with the production of filamentary materials, having a basisof cellulose acetate, which is commercially the most important organicacid ester of cellulose at the present time. It may also be employed forthe production of filamentary materials having a basis of other organicacid esters of cellulose, such as, cellulose propionate, cellulosebutyrate, cellulose acetate propionate and cellulose acetate butyrate.

The following examples are given to illustrate this invention further.

Exqmple I Dope containing 26% by weight of cellulose acetate dissolvedin acetone is spun into a coagulating medium containing 85% by volume ofmethylene chloride and 15% by volume of carbon tetrachloride maintainedat a temperature of 25 C. The filamentary materials travel- Example 11Dope containing 25% by weight of cellulose acetate, having an acetylvalue of 54.6%, calculated as acetic acid, dissolved in acetone, is spuninto a coagulating medium. containing 82.5% by volume of methylenechloride and 17.5 by volume of carbon tetrachloride maintained at atemperature of 25 C. The filamentary materials travel through saidcoagulating medium for a distance of 9 inches and are stretched toincrease their length 2200%. The filamentary materials then travelthrough a 3 inch layer of 20% aqueous ammonium hydroxide which isfloate'd upon the surface of the coagulat- 4 ing medium. Upon emergingfrom the coagulating medium, the filamentary materials are washed anddried and are then wound onto a spool at a rate of 81 meters per minute.The filamentary materials are partially saponified and have an averageacetyl value of 48%, calculated as acetic acid, and exhibit a tenacityof 3.24 grams per denier and an elongation of 16.4% at the breakingpoint.

Example III The process set forth in Example I is repeated, employing asa coagulating medium a mixture of 95% by weight of ethylene chloride and5% by weight of carbon tetrachloride, and taking up the filamentarymaterials at a rate of 97 meters per minute. The filamentary materialsexhibit a tenacity of 2 grams per denier and an elongation of 43% at thebreaking point.

Example I V' The process set forth in Example I is repeated, employingas a coagulating medium a mixture of 82.5% by weight of methylenechloride and 17.5% by weight of cyclohexane, and taking up thefilamentary materials at a rate of 68 meters per minute. The filamentarymaterials exhibit a tenacity of 3.5 grams per denier and an elongationof 22% at the breaking point.

It is to be understood that the foregoing detailed description is givenmerely by way of illustration and that many variations may be madetherein without departing from the spirit of my invention.

Having described my invention, what I desireto secure by Letters Patentis:

Process for the production of filamentary materials which comprisesspinning a solution containing 25% by weight of cellulose acetate havingan acetyl value of 54.6% dissolved in acetone into a coagulating mediummaintained at 25 C. and containing 82.5% by volume of methylene chlorideand 17.5% by volume of carbon tetrachloride, stretching the filamentarymaterials to increase their length 2200% while they travel through saidcoagulating medium for a distance of 9 inches, then passing saidfilamentary materials through a 3 inch layer of 20% aqueous ammoniumhydroxide which isfioated 0n the coagulating medium to reduce theaverage acetyl value of the cellulose acetate to 48%, washing and dryingthe filamentary materials, and taking up the filamentary materials at arate of 81 meters per minute.

References Cited in the file of this patent

